The DCCT demonstrated that intensive diabetes therapy prevents the onset or slows the progression of the long-term complications of type 1 diabetes. Yet, intensive diabetes therapy as implemented in the DCCT was associated with a 3-fold increase in the risk of severe hypoglycemia, which is presumed to be a trigger of cardiac arrhythmias and subsequent sudden death. Additional risk factors for the development of arrhythmias include cardiovascular autonomic neuropathy, genetic predisposition, and coronary artery disease; all of which have been assessed in the DCCT/EDIC cohort over time. To more fully understand the relationship of hypoglycemia and disturbances in cardiac rhythm, we propose to monitor the electrocardiogram and glucose levels for one week in at least 1,200 of the surviving DCCT/EDIC participants with the following objectives: 1) to determine the effects of hypoglycemia on the risk of ventricular and other arrhythmias in patients with type 1 diabetes; 2) to characterize the phenotype of those patients with type 1 diabetes with the highest risk for arrhythmia in the presence of hypoglycemia. The information uncovered through this proposal will guide clinicians in their individualized management of patients with type 1 diabetes to prevent catastrophic sudden death.